Large format document scanners, i.e. those for scanning documents of widths greater than approximately 11 inches, employ a plurality of imaging elements. The imaging elements are so arranged that, in use, each element generates image data representative of a portion of a scan line of a document. Each portion of the scan line has a slight overlap with one to two other portions, dependent on whether the portion is from an end or the middle of the scan line. In a known method of generating image data representative of the entire scan line from the image data from a plurality of imaging elements, an initial and/or terminal portion of the image data from each imaging element, corresponding to the slight overlap or overlaps, is discarded, and the remainders of the image data are concatenated with one another.
The known method assumes that a distance from the document to the imaging elements is constant, and that the slight overlaps of the portions of the scan line are therefore also constant, and an initial and/or terminal portion of a predetermined length of the image data from each element is discarded. However, due to imperfections of a process by which the document is moved relative to the imaging elements or vice versa, or due to imperfections of the document itself, such as folds that cannot be completely flattened, the distance from the document to the imaging elements, and hence the slight overlaps of the portions of the scan line, are variable. If the distance from the document to the imaging elements increases, discarding a portion of the image data of the predetermined length results in duplication of data in the image data representative of the entire scan line, and hence duplication of some portions in a resulting image of the scan line. Where the distance from the document to the imaging elements decreases, discarding a portion of the image data of the predetermined length results in deletion of data from the image data representative of the entire scan line, and hence, omission of some portions in a resulting image of the scan line. FIG. 1 of the attached drawing figures illustrates the effects of variation of distance from the document to the scanning elements when the known document scanning method is employed.